As will be apparent from the earlier publications and applications mentioned previously, mixing heads for intimately mixing two or more interreactive synthetic resin components, wherein resin components are directed in respective streams against one another into a mixing chamber so that the streams impinge upon one another, have been provided heretofore. Among the reactive systems for which such heads can be used, is the anionic polymerization of caprolactam.
From the prior patents listed, it should be apparent that an important characteristic of these mixing heads is the presence of a control member or piston which, upon retraction, unblocks the ports admitting the oppositely directed streams of the reactants to the mixing chamber and, when advanced, blocks the ports and drives the mixing procedure from the mixing chamber.
The position in which the ports are unblocked and the mixing chamber is left clear to permit intermingling and interaction of the reactive components is referred to as the mixing phase or position, and the position in which the ports are blocked and the residue is completely expelled from the chamber is referred to as the nonmixing phase or position. In the latter phase, the end face of the piston may lie flush with the end of the mixing chamber bore.
These two phases will be readily appreciated with reference to German Pat. No. 20 07 935.
Especially when one works with caprolactam, one finds a tendency for premature reaction because of the especially high mixing and reactive tendencies of the components. This can give rise to problems. For example, if just prior to blockage of the ports or orifices and entry into the nonmixing phase, even miniscule amounts of one component enter the port of the other component, during the subsequent nonmixing phase the reaction at this port will block the latter or even generate a prereacted particle, droplet or slug of material which, if driven into the mold, will detrimentally affect the uniformity of the next product made.
Thus in some cases, there is total or partial blockage of one or both of the ports because of the inability to completely prevent traces from one material with mixing with the other within the port just prior to blockage of the ports. Even if the ports are not blocked, the reacted materials create defects in the subsequent product. Finally, partial or complete obstruction of one or both of the ports may result in defective products because of changes in the proportions of the two components in the mixture which ultimately reaches the mold.